U.S. patent number 6,067,495 [Application Number 08/881,119] was granted by the patent office on 2000-05-23 for acceleration based shift strategy for an automatic transmission.
This patent grant is currently assigned to Chrysler Corporation. Invention is credited to Steven R. Fliearman, Mark R. Foeller, Kenneth J. Potter, Dennis Zeiger.
United States Patent |
6,067,495 |
Fliearman , et al. |
May 23, 2000 |
Acceleration based shift strategy for an automatic transmission
Abstract
An shift control strategy for controlling an automatic
transmission based on acceleration. The shift control strategy
determines a learned vehicle inertia as well as road load torque
and expected torque in an upshift gear. A projected post shift
acceleration is predicted based on the expected torque, road load
torque and inertia of the vehicle. If vehicle speed and throttle
position are within an allowable shift zone and if the predicted
post shift acceleration exceeds a threshold value, the vehicle
automatic transmission is allowed to upshift. The predicted post
upshift acceleration value is determined as a function of a
selected one of the possible downshifts and is compared to a
threshold value. A downshift of the automatic transmission to the
selected downshift is allowed if the post downshift acceleration
value is less than the threshold value.
Inventors: |
Fliearman; Steven R. (Howell,
MI), Foeller; Mark R. (Grass Lake, MI), Potter; Kenneth
J. (Almont, MI), Zeiger; Dennis (Royal Oak, MI) |
Assignee: |
Chrysler Corporation (Auburn
Hills, MI)
|
Family
ID: |
25377823 |
Appl.
No.: |
08/881,119 |
Filed: |
June 24, 1997 |
Current U.S.
Class: |
701/55; 477/108;
477/120; 701/56; 701/64; 74/335; 74/336R |
Current CPC
Class: |
F16H
61/0213 (20130101); F16H 59/48 (20130101); F16H
59/52 (20130101); F16H 2061/0216 (20130101); Y10T
74/1926 (20150115); Y10T 74/19251 (20150115); Y10T
477/692 (20150115); Y10T 477/676 (20150115) |
Current International
Class: |
F16H
61/02 (20060101); F16H 59/52 (20060101); F16H
59/50 (20060101); F16H 59/48 (20060101); G06G
007/70 (); B60K 041/04 () |
Field of
Search: |
;701/51,52,55,53,58,66,93,62,65,54 ;477/108,148,149,110,120,133,155
;74/335,336R |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
4875391 |
October 1989 |
Leising et al. |
4905545 |
March 1990 |
Leising et al. |
4951200 |
August 1990 |
Leising et al. |
5241476 |
August 1993 |
Benford et al. |
5245893 |
September 1993 |
Koening et al. |
5669580 |
September 1997 |
Dourra et al. |
5685801 |
November 1997 |
Benford et al. |
5738605 |
April 1998 |
Fliearman et al. |
5778331 |
July 1998 |
Leising et al. |
5794170 |
August 1998 |
Kuroda et al. |
|
Primary Examiner: Louis-Jacques; Jacques H.
Attorney, Agent or Firm: Calcaterra; Mark P.
Claims
What is claimed is:
1. A method of adaptively controlling transmission gear upshifts in
an automatic transmission of a vehicle, said method comprising the
steps of:
determining a vehicle inertia;
determining if a current acceleration is less than a downshift
acceleration threshold and, if not, obtaining an upshift
acceleration threshold based on reflected inertia of said vehicle
and a throttle opening of a throttle of said vehicle;
determining if a calculated projected acceleration is greater than
said obtained upshift acceleration threshold;
if said calculated projected acceleration is greater than said
upshift acceleration threshold, then determining if an upshift will
be within an allowable shift zone and, if so, extending said
upshift.
2. A method of adaptively controlling transmission gear downshifts
in an automatic transmission of a vehicle, said method comprising
the steps of:
determining output torque of an automatic transmission;
determining a learned vehicle inertia;
determining if a current acceleration of said vehicle is less than
a downshift acceleration threshold and, if so, determining a
projected gear based on said determined torque output, calculating
projected acceleration based on said learned vehicle inertia and
said proiected gear, and determining if said projected acceleration
is greater than said downshift acceleration threshold;
if said projected acceleration is greater than said downshift
acceleration threshold, then determining if a shift can be made
which is within an allowable shift zone and, if so, executing said
shift.
3. The method as defined in claim 2 wherein when the predicted post
shift acceleration is not within a desired range the method further
comprises the steps of:
selecting the next possible downshift from a hierarchy table;
predicting an expected post shift acceleration for the next
selected one of the upshifts;
comparing the predicted post shift acceleration of the next
selected downshift to a threshold value; and
initiating a transmission downshift as a function of the step of
comparing the post shift acceleration to the next selected
downshift.
4. A method of adaptively controlling transmission gearshifts in an
automatic transmission of a vehicle, said method comprising the
steps of:
determining output torque of an automatic transmission;
determining a learned vehicle inertia;
determining if a current acceleration is less than a downshift
acceleration threshold and, if not, obtaining an upshift
acceleration threshold based on vehicle speed, a throttle opening
of a throttle of said vehicle and said learned vehicle inertia;
selecting possible upshifts one at a time from an upshift hierarchy
table in an ordered sequence;
predicting an expected post upshift acceleration for the selected
one of the upshifts from the upshift hierarchy table;
comparing the predicted post upshift acceleration of the selected
upshift to an upshift threshold value;
initiating a transmission upshift to the selected upshift when the
predicted post upshift acceleration exceeds the upshift threshold
value;
selecting possible downshifts one at a time from a downshift
hierarchy table in an ordered sequence;
predicting an expected post downshift acceleration for the selected
one of the downshifts from the downshift hierarchy table;
comparing the predicted post downshift acceleration to a downshift
threshold value; and
initiating a transmission downshift to the selected downshift when
the predicted post downshift acceleration value is greater than the
downshift threshold value.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates generally to automatic transmission
control for an automotive vehicle and, more particularly, to an
acceleration based shift control strategy for controlling the gear
shifting of an automatic transmission.
2. Discussion
Automotive vehicles generally incorporate a motive force system
having three basic components: an engine, a powertrain and wheels.
The engine produces force by converting chemical energy from a
liquid fuel into the mechanical energy of motion. The powertrain
transmits the resultant force of this kinetic energy to the wheels
which frictionally contact a surface for moving the vehicle. The
main component of the powertrain is the transmission, which
transmits engine torque over a relatively limited angular speed
range to the wheels over a broader speed range, in accordance with
the tractive-power demand of the vehicle. The transmission also
controls the direction of rotation applied to the wheels so that
the vehicle may be driven both forward and backward.
One advanced type of transmission is a four speed electronically
controlled automatic transmission with overdrive. Examples of this
type of electronically controlled automatic transmission are
described in U.S. Pat. No. 4,875,391, entitled "An
Electronically-Controlled, Adaptive Automatic Transmission System",
issued on Oct. 24, 1989 to Leising et al; U.S. Pat. No. 4,905,545,
entitled "Method of Controlling the Speed Change of a Kickdown
Shift for an Electronic Transmission System", issued on Mar. 6,
1990 to Leising et al and U.S. Pat. No. 4,951,200, entitled "Method
of Controlling the Apply Element During a Kickdown Shift for an
Electronic Automatic Transmission System", issued on Aug. 21, 1990
to Leising et al. These patents are owned by the Assignee of the
present application and are incorporated herein by reference.
However, it should be appreciated that the principles of the
present invention are not limited to any particular automatic
transmission, whether electronic or hydraulic controlled and that
the present invention may be applied to a wide variety of other
powertrain configurations.
Automotive vehicles are commonly equipped with electronic control
systems such as a powertrain control system for controlling the
operation of the engine and drivetrain of the vehicle. The
electronic powertrain control system includes a microcomputer-based
transmission controller capable of receiving and monitoring input
signals indicative of various vehicle operating conditions such as
engine speed, torque converter turbine speed, output vehicle speed,
throttle angle position, brake application, hydraulic pressures, a
driver selected gear or operating condition (PRNDL), engine coolant
temperature and/or the ambient air temperature. Based on the
information contained in the monitored signals, the
controller generates command or control signals for causing
actuation of solenoid-actuated valves to regulate the application
and release of fluid pressure to and from apply cavities of
clutches or frictional elements of the transmission. Accordingly,
the transmission controller is typically programmed to execute
predetermined shift schedules stored in memory of the controller
through appropriate command signals to the solenoid-actuated
valves.
In some conventional automatic transmission control routines, the
use of a predetermined shift schedule provides allowable gear
shifts based on a speed value and percentage of throttle opening.
An automatic transmission gear upshift generally follows a
predetermined upshift curve, while a transmission downshift follows
a predetermined downshift curve. The upshift and downshift shift
points are determined as a function of output shaft speed and
percentage of throttle opening and are commonly obtained from the
upshift and downshift curves. With the conventional approach, the
shift points remain constant as long as the vehicle can maintain
the desired shift speed.
Conventional automatic transmission gear shifting approaches
provide shift points that compromise for various possible loads on
a vehicle. For example, a vehicle that is lightly loaded may
realize a shift point that occurs later than desired because of
compromises taken into consideration for heavier vehicle loading
conditions. Moreover, this problem is amplified for downhill
vehicle travel conditions. Similarly, for a vehicle that is heavily
loaded, the shift points are generally compromised for lighter
vehicle loading conditions, and this may result in lugging of the
engine. This is especially true for heavily loaded vehicles
traveling uphill and can lead to a gear "shift hunting" condition
in which an upshift gear does not provide sufficient torque to
maintain vehicle speed and results in cyclical upshift and
downshift gear changes.
It is therefore one object of the present invention to provide for
a system and method of controlling gear shifting of an automatic
transmission for a motor vehicle in a manner that is adaptive to
vehicle loading conditions.
It is another object of the present invention to provide for such a
system and method of controlling automatic transmission upshifts
that adapts to heavy vehicle load increases.
It is also an object of the present invention to provide for such a
system and method of controlling downshifting of the automatic
transmission taking into consideration lessened vehicle load
conditions.
Further, it is another object of the present invention to monitor
torque and vehicle load and predict available acceleration to
control transmission gear shifting of an automatic transmission to
accommodate for different load conditions on the vehicle.
SUMMARY OF THE INVENTION
To achieve the foregoing objectives, the present invention is an
adaptive transmission control strategy for controlling shifting of
an automatic transmission of a vehicle to accommodate various loads
on the vehicle. Following stopping of the vehicle, an approximate
learned vehicle inertia is determined and used to determine road
load torque. With the automatic transmission engaged in a lower
gear, the output torque is determined for the lower gear and a
predicted torque available in an upshift condition of the
transmission to an upper gear is determined. Projected post shift
acceleration available in the upper gear is predicted and compared
with a threshold value. Provided the shift schedule point is within
an allowable shift zone and if the predicted post shift
acceleration value exceeds the threshold value, the automatic
transmission shifts to the upshift gear. For a downshift, projected
downshift acceleration is predicted for a selected one of the
possible downshifts and is compared to a threshold value. Provided
the shift schedule point is within an allowable shift zone and if
the predicted post shift deceleration value is less than the
threshold value, the automatic transmission shifts to the selected
downshift gear.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the present invention will become
apparent to those skilled in the art upon reading the following
detailed description and upon reference to the drawings in
which:
FIG. 1 is a block diagram illustrating a vehicle equipped with an
automatic transmission controlled in accordance with an adaptive
acceleration based shift control strategy according to the present
invention;
FIG. 2 is a three-dimensional look-up surface which provides
turbine torque based on turbine speed and throttle opening
percentage;
FIG. 3 is a graphical representation of allowable shift zones for
an automatic transmission of a vehicle as a function of output
shaft speed and throttle opening percentage;
FIG. 4 is a three-dimensional look-up surface which illustrates the
allowable shift points for an upshift of the transmission as a
function of acceleration, output speed and throttle opening
percentage; and
FIGS. 5 and 5A together provide a flow diagram illustrating an
acceleration based shift control strategy for an automatic
transmission in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning now to FIG. 1, a vehicle 10 is provided as a block equipped
with an automatic transmission 12 that is controlled so as to shift
the automatic transmission among the available gear shifts. The
automatic transmission 12 is advantageously controlled in
accordance with an acceleration based shift control routine which
monitors acceleration, torque and load, predicts the availability
of post shift acceleration and determines the appropriate upshift
and downshift shift points of the automatic transmission. While the
present invention is described herein in connection with an
electronic or hydraulic controlled four-speed transmission, it
should be appreciated that various other automatic transmissions
may be employed in connection with the shift control strategy of
the present invention.
The vehicle's powertrain control unit 16 is in communication with
the automatic transmission 12. The powertrain control unit 16
preferably is microprocessor-based and includes memory which
contains the shift control routines for determining gear shift
points and controlling gear shifting of the automatic transmission
12. While the powertrain control unit 16 is described as containing
the acceleration based shift control routine and other transmission
control routines, it should be appreciated that the shift control
routine and other transmission control routines could alternately
be provided in other control devices such as a transmission control
module.
The powertrain control unit 16 receives various vehicle parameters
and determines the shift points for initiating gear shifts of the
automatic transmission 12 based upon a predetermined shift
schedule, as well as upshift and downshift control routines
provided with the shift control routine of the present invention.
In doing so, the powertrain control unit 16 outputs a shift control
signal 15 to the automatic transmission 12 to control upshifting
and downshifting of the automatic transmission 12.
The vehicle 10 is equipped with output shaft speed sensor 18,
turbine speed sensor 20 and driver selected transmission position
(PRNDL) sensor 22. Each of sensors 18, 20 and 22 senses signals
associated with the automatic transmission 12 and provides an
output to the powertrain control unit 16. Output shaft speed sensor
18 provides an indication of the rotational speed of the
transmission output shaft, while the turbine speed sensor 20
provides an indication of the rotational speed of the turbine
output shaft of the transmission. The driver selected transmission
position sensor 22 provides an indication of the manually
selectable transmission operating mode. The powertrain control unit
16 also receives an input from a brake switch sensor 24 which
provides a brake actuation signal. Further, powertrain control unit
16 receives a signal from a throttle position sensor 14 which is
indicative of the position of the throttle that is controlled in
response to either driver actuation of the accelerator pedal or a
cruise control system, if employed.
It should be appreciated that the powertrain control unit 16
typically receives various other inputs such as coolant
temperature, ambient temperature, battery, distributor and ignition
switch information as is generally provided to the powertrain
control unit in a motor vehicle. It should also be understood that
the powertrain control unit 16, or a transmission control module
(not shown), typically receives various other signals such as a
pressure switch input, a manifold absolute pressure (MAP) signal,
cruise control signals and vehicle speed signals. It should further
be appreciated that various signals could be received via a
communication line or network such as a Chrysler Collision
Detection (CCD) network and such a network may interconnect a
transmission control module with the powertrain control unit
16.
The powertrain control unit 16 further receives a converted turbine
torque signal from a torque turbine mapped surface 26 with air
density compensation which is converted via a gear ratio converter
28. Powertrain control unit 16 also receives a shift choices signal
from shift hierarchy table 36 which provides an ordered selection
of available gear shifts. Allowable shifts block 34 determines
which gear shifts are available based on the received current gear
position from block 32 and a shift zone table 30, and passes the
allowable shifts onto shift hierarchy table 36 for consideration
therewith. In addition, powertrain control unit 16 receives a
downshift acceleration signal from downshift acceleration surface
38 and an upshift acceleration signal from upshift acceleration
surface 40. The shift hierarchy table 36, turbine torque mapped
surface 26 and shift zone table 30, as well as downshift
acceleration surface 38 and upshift acceleration surface 40 are
provided in mapped surfaces or tables as will be explained
hereinafter.
The shift hierarchy table 36 includes both an upshift hierarchy
table and a downshift hierarchy table. One example of an upshift
hierarchy table is provided as follows:
______________________________________ UPSHIFT HIERARCHY PRIORITY
CURRENT GEAR INDEX 1 2 2L 3 3L 4 4L
______________________________________ 1 3L 4L 4L 4L 4L 4L 4L 2 3 4
4 4 4 4 4L 3 2L 3L 3L 3L 3L 4 4L 4 2 3 3 3 3L 4 4L 5 1 2L 2L 3 3L 4
4L 6 1 2 2L 3 3L 4 4L ______________________________________
The upshift hierarchy table provides ordered priority of available
gear shift selections for each of the potential current gears. The
upshift hierarchy table lists in prioritized order the possible
upshifts that can be considered. For example, with the current gear
being second gear, the upshift hierarchy table will first look to
see if an upshift to fourth gear lock (e.g., with the converter
clutch locked) is appropriate. In decreasing order, the upshift
hierarchy table provides subsequent consecutive choices of fourth
gear, third gear lock, third gear, second gear lock, and lastly
currently engaged second gear.
One example of a downshift hierarchy table is provided as
follows:
______________________________________ DOWNSHIFT HIERARCHY PRIORITY
CURRENT GEAR INDEX 1 2 2L 3 3L 4 4L
______________________________________ 1 1 1 2 2L 3 3L 4 2 1 1 1 2
2L 3 3L 3 1 1 1 1 2 2L 3 4 1 1 1 1 1 2 2L 5 1 1 1 1 1 1 2 6 1 1 1 1
1 1 1 ______________________________________
The downshift hierarchy table likewise provides an ordered priority
of transmission gear downshifts for each of the potential current
gears. The downshift hierarchy table lists in prioritized order the
possible downshifts that can be considered. For example, when
engaged in fourth gear, the downshift hierarchy table prioritizes
potential gear shifts as follows: third gear lock, third gear,
second gear lock, second gear, and lastly considers first gear. The
priority for upshifting and downshifting preferably takes into
consideration adequate achievable acceleration or deceleration and
fuel economy. While examples of upshift and downshift hierarchy
tables are provided above, it should be appreciated that other
prioritized gear shift orders may be provided.
The turbine torque mapped surface 26 is shown in greater detail in
FIG. 2. Turbine torque mapped surface 26 is a three-dimensional
surface containing stored turbine torque (LB-FT) values based on
turbine speed (RPM) and throttle percentage opening . Given the
turbine speed and throttle opening percentage, the appropriate
turbine torque can be looked up from turbine torque mapped surface
26. The determined turbine torque value is then converted by the
gear ratio converter 28 and thereafter supplied to the powertrain
control unit 16 as an output torque signal. The input turbine
torque is therefore converted in accordance with the gear ratio to
provide an output value indicative of the transmission output
torque.
With particular reference to FIG. 3, one example of a shift zone
table 30 is illustrated therein. Shift zone table 30 shows shift
zones for each of the transmission gears as a function of output
shaft speed and throttle percentage opening. The shift zone for
first gear is defined by the region to the left of line 42. The
region between lines 44 defines the allowable shift zone for second
gear, while the region between lines 48 defines the allowable shift
zone for third gear. The allowable shift zone for fourth gear is
defined by the region to the right of line 52. The automatic
transmission as described herein includes a converter clutch for
providing converter lockup. Accordingly, shift points are provided
as shown herein for the converter clutch lockup based on a full
lock torque value. The allowable shift zone for a second gear
converter clutch lockup is defined by the region between lines 46,
while the allowable shift zone for a third gear converter clutch
lockup is defined by the region between lines 50. Finally, the
allowable shift zone for a fourth gear converter clutch lockup is
defined by the region to the right of line 54. Accordingly, the
automatic transmission may shift among the available gears which
include first gear through fourth gear as well as converter lockups
for second gear through fourth gear. It should be appreciated that
reference to a gear shift may include a shift between gears, a
shift between a gear with the converter unlocked and a gear lockup
or a shift between gear lockups. Available gear shifts are limited
to the region provided by the allowable shift zones as defined in
the shift zone table 30 of FIG. 3.
FIG. 4 illustrates one example of an upshift acceleration surface
40. The upshift acceleration surface 40 provides an acceleration
threshold value which may be looked up as a function of the
throttle percentage opening and turbine output speed as monitored
on the vehicle. The acceleration threshold value is then compared
with a projected acceleration value to determine whether a upshift
of the automatic transmission is appropriate. Similarly, the
downshift acceleration surface 38 likewise provides an acceleration
threshold value as a function of throttle percentage opening and
turbine output speed. The downshift acceleration surface 38
acceleration threshold value is compared to the current
acceleration to determine whether a downshift of the automatic
transmission is appropriate.
Referring to FIGS. 5 and 5A, an acceleration based shift control
methodology 60 is illustrated for determining upshift and downshift
shift points and controlling gear shifting of the automatic
transmission in accordance with the present invention. Shift
control methodology 60 uses sensed vehicle parameters and
repeatedly calculates the output shaft
acceleration .alpha..sub.n for the current engaged transmission
gear (n) as provided in block 62. Shift control methodology 60 also
calculates transmission input torque. Shift control methodology 60
further calculates the vehicle road load torque T.sub.RL at the
transmission output shaft as a function of the difference between
the product of calculated transmission input torque and the current
gear ratio and the product of the current acceleration and vehicle
reflected inertia (I). Vehicle reflected inertia (I) as well as
road load torque T.sub.RL can be determined as described in
co-pending U.S. patent application Ser. No. 08/672,883, entitled
"Anti-Hunt Strategy for an Automatic Transmission", filed on Jun.
28, 1996 and assigned to the Assignee of the present application.
The aforementioned pending U.S. patent application is incorporated
herein by reference.
Shift control methodology 60 initially determines a learned vehicle
reflected inertia (I) while the automatic transmission is
performing a transmission gear upshift. The optimal condition for
determining vehicle inertia is found to be under conditions where a
significant change in output torque occurs while the road load
remains relatively constant. A change in gear ratio during a
transmission shift meets these requirements with a sharp change in
output torque that is determined by a look-up table. Shift control
methodology 60 initially determines a learned vehicle inertia (I)
while the automatic transmission is performing a transmission gear
upshift. According to a preferred embodiment, shift control
methodology 60 will determine vehicle inertia (I) during the first
transmission gear upshift from first gear to second gear (e.g., 1-2
upshift) following each time the vehicle is stopped. Therefore, the
learned vehicle inertia I adapts to changes in inertia as
determined after each vehicle stop.
To determine vehicle inertia (I), shift control methodology 60 will
check to see if a first gear-to-second gear (1-2) upshift is
currently in progress. If the 1-2 upshift is detected, shift
control methodology 60 proceeds to check to see if the second gear
has been detected. If second gear has not yet been detected, the
strategy will check to see if the 1-2 shift has just started and,
if so, shift control methodology 60 will calculate output torque
(T.sub.n) for the currently engaged transmission gear (n), and
thereafter will store the output shaft torque T.sub.n and
acceleration .alpha..sub.n in memory. The output torque T.sub.n as
referred to herein is the torque at the output of the transmission.
The transmission input torque is determinable from the output
torque and gear ratio.
Once second gear has been detected, shift control methodology 60
checks if a timer has expired. The timer provides a time delay
during which the abrupt transmission gear transition generally is
known to occur which causes disturbance of the output torque that
is to be avoided in the measurement. Once the timer has expired,
shift control methodology 60 calculates the output shaft torque
T.sub.n+1 for the upshift gear (n+1). Output shaft torque T.sub.n+1
is the output shaft torque calculated for the transmission gear
upshift which in this case is second gear. Thereafter, shift
control methodology 60 will calculate vehicle inertia I. Vehicle
inertia I can be calculated by dividing the difference in output
torque in first gear and second gear represented by (T.sub.n
-T.sub.n+1) by the difference in acceleration in the first gear and
second gear represented by (.alpha..sub.n -.alpha..sub.n+1). These
torque and acceleration measurements are preferably taken in first
gear just prior to the upshift and in second gear just after the
upshift occurs. It is preferred that the measurements be taken
during the shortest time period possible without realizing effects
caused by the shift induced disturbance. This also allows the
assumption of a constant road load torque T.sub.RL.
Once the vehicle inertia I has been determined, the road load
torque T.sub.RL at the transmission output shaft can be calculated.
The torque T.sub.n at the transmission output shaft is equal to the
product of vehicle inertia I and acceleration .alpha..sub.n summed
with road load torque T.sub.RL. Road load torque T.sub.RL generally
includes torque losses which take into consideration aerodynamic
drag of the vehicle, rolling resistance of the tires and frictional
losses in the drivetrain as well as the grade of the road that the
vehicle is traveling on. In effect, the output torque from the
transmission will be consumed by the road load torque or be
expressed as an acceleration of the output shaft.
Proceeding to block 64, shift control methodology 60 looks up a
downshift acceleration threshold value based on turbine output
speed, the throttle percentage opening and calculated vehicle
reflected inertia. Next, shift control methodology 60 will
initialize variables by setting a pointer equal to one and setting
the desired gear to the current gear as provided in block 66. Shift
control methodology 60 will then proceed to decision block 68 to
compare the calculated current acceleration with the looked up
downshift acceleration threshold value. If the calculated current
acceleration is equal to or greater than the looked up downshift
acceleration threshold value, methodology 60 proceeds to block 70
to look up the upshift acceleration threshold value based on
turbine output speed, throttle percentage opening and vehicle
reflected inertia. Methodology 60 will also look up the projected
gear based on the pointer and the current gear as provided in block
72. Decision block 74 checks for whether the projected gear is
equal to the current gear of the automatic transmission and, if so,
no shift is necessary and methodology 60 proceeds to continue block
86. Otherwise, if the projected gear is not equal to the current
gear, shift control methodology 60 proceeds to block 76 in which
the projected acceleration is calculated as a function of the
difference between projected output torque and road load torque
divided by the vehicle reflected inertia.
Methodology 60 then compares the projected acceleration to the
upshift acceleration threshold as provided in decision block 78. If
the projected acceleration is less than or equal to the upshift
acceleration threshold, methodology 60 proceeds to increment the
pointer by one and to set the desired gear equal to the projected
gear as provided in block 88 and then proceeds to block 72.
Otherwise, if the projected acceleration is greater than the
upshift acceleration threshold, methodology 60 will proceed to
block 80 to look up the allowable shift zone based on output shaft
speed and throttle percentage opening. Decision block 90 then
checks to see if the gear shift is within the allowable limits of
the shift zone, and if not proceeds to block 88. Otherwise, if the
shift is within the allowable limits, methodology 60 proceeds to
block 92 to set the desired gear equal to the projected gear.
Thereafter, decision block 82 performs a check to see if the
desired gear has already been set equal to the current gear and, if
so, is complete and proceeds to continue block 86. Otherwise,
methodology 60 schedules a shift pursuant to block 84 and is
thereafter complete pursuant to continue block 86.
Referring back to decision block 68, if the calculated current
acceleration is determined to be less than the downshift
acceleration threshold, methodology 60 proceeds to block 94 to look
up the projected gear based on the pointer and the current gear.
The projected gear is compared with the current gear as provided in
decision block 96. If the projected gear is equal to the current
gear, shift control methodology 60 is complete and proceeds to
continue block 86. Otherwise, if the projected gear is not equal to
the current gear, methodology 60 will proceed to calculate the
projected acceleration as a function of the difference between
projected output torque and road load torque divided by the vehicle
reflected inertia as provided block 98. Thereafter, decision block
100 compares the projected acceleration with the downshift
acceleration threshold. If the projected acceleration is greater
than the downshift acceleration threshold, the pointer is
incremented and the desired gear is set equal to the projected gear
as provided in block 102, and methodology 60 thereafter proceeds
back to block 94. Otherwise, if the projected acceleration is equal
to or less than the desired acceleration, methodology 60 will
proceed to look up the allowable shift zone based on output shaft
speed and throttle percentage opening as provided in block 104.
Thereafter, decision block 106 checks to see if the projected gear
shift is within the allowable limits as determined by the allowable
shift zone and, if so, proceeds to block 92. Otherwise, if the
shift is not within the allowable shift limits, methodology 60
proceeds to decrement the pointer as provided in block 108 and
thereafter decision block 110 checks to see if the pointer is less
than a value of one. If the pointer has decremented to a value of
less than one, methodology 60 is complete and proceeds to continue
block 86. Otherwise, methodology 60 proceeds to block 112 to look
up the projected gear based on the pointer and the current gear and
thereafter proceeds to block 104.
In operation, the shift control methodology 60 will detect when the
vehicle is stopped and thereafter calculate the vehicle inertia I.
This is accomplished by looking up the output shaft torque in first
gear just prior to an upshift and looking up torque in the upshift
gear just after the upshift occurs. Likewise, acceleration is
measured in first gear just prior to an upshift and also just after
the upshift occurs to second gear. Vehicle inertia is then
calculated as a difference in torque divided by the difference in
acceleration. To account for vehicle losses, shift control
methodology 60 calculates a road load torque as a function of the
output shaft torque, vehicle inertia and acceleration.
Shift control methodology 60 determines post shift acceleration for
either an upshift or a downshift for the next upshift or downshift
gears to be considered. Methodology 60 looks to a prioritized table
for upshift gears and a prioritized table for downshift gears and
determines whether the acceleration either positive or negative,
that is achievable is acceptable for the currently considered gear.
While methodology 60 looks at acceleration, the acceleration may be
either a positive or negative value. If an upshift or a downshift
is allowable, the gear shift may occur.
While a specific embodiment of the invention has been shown and
described in detail to illustrate the principles of the present
invention, it should be understood that the invention may be
embodied otherwise without departing from such principles. For
example, one skilled in the art will readily recognize from such
discussion and from the accompanying drawings that various changes,
modifications and variations can be made without departing from the
spirit and scope of the present invention as described in the
following claims.
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